The invention relates to fluid-flow responsive devices which produce an electrical output in response to such flow.
So far as we are aware, past devices of the character indicated employ a valve-member element which is displaced in response to fluid flow, and a predetermined displacement is monitored by an on/off electrical element, such as a magnetic-reed switch. Such devices are exemplified by U.S. Pat. Nos. 2,892,051 and 4,081,635. Necessarily, such devices are limited as indicators of the onset or existence of a pre-specified flow rate, and the only way to obtain response to more than one flow rate is to employ more than one magnetic switch, at one or more further locations selected to be measures of the respective further flow rates for which electrical response is desired. At best, only a step-function response is achievable, and a hysteresis factor is present to preclude identity as between the electrical response to increasing flow-rate conditions, when compared to the electrical response to decreasing flow-rate conditions.